1. Field of the Invention
The present invention relates to the extraction and purification of flavonoid compounds from plant material, and more specifically to the production of compositions enriched in total phenols.
2. Description of the Prior Art
Flavonoid compounds are present in all aerial parts of plants, with high concentrations found in the skin, bark, and seeds. Such compounds are also found in numerous beverages of botanical origin, such as tea, cocoa, and wine. The flavonoids are a member of a larger family of compounds called polyphenols. That is, these compounds contain more than one hydroxyl group (OH) on one or more aromatic rings. The physical and chemical properties, analysis, and biological activities of polyphenols and particularly flavonoids have been studied for many years.
Anthocyanins are a particular class of naturally occurring flavonoid compounds that are responsible for the red, purple, and blue colors of many fruits, vegetables, cereal grains, and flowers. For example, the colors of fruits such as blueberries, bilberries, strawberries, raspberries, boysenberries, marionberries, cranberries, elderberries, etc. are due to many different anthocyanins. Over 300 structurally distinct anthocyanins have been identified in nature. Because anthocyanins are naturally occurring, they have attracted much interest for use as colorants for foods and beverages.
Recently, the interest in anthocyanin pigments has intensified because of their possible health benefits as dietary antioxidants. For example, anthocyanin pigments of bilberries (Vaccinium myrtillus) have long been used for improving visual acuity and treating circulatory disorders. There is experimental evidence that certain anthocyanins and other flavonoids have anti-inflammatory properties. In addition, there are reports that orally administered anthocyanins are beneficial for treating diabetes and ulcers and may have antiviral and antimicrobial activities. The chemical basis for these desirable properties of flavonoids is believed to be related to their antioxidant capacity. Thus, the antioxidant characteristics associated with berries and other fruits and vegetables have been attributed to their anthocyanin content.
Proanthocyanidins, also known as “oligomeric proanthocyanidins,” “OPCs,” or “procyanidins,” are another class of naturally occurring flavonoid compounds widely available in fruits, vegetables, nuts, seeds, flowers, and barks. Proanthocyanidins belong to the category known as condensed tannins. They are the most common type of tannins found in fruits and vegetables, and are present in large quantities in the seeds and skins. In nature, mixtures of different proanthocyanidins are commonly found together, ranging from individual units to complex molecules (oligomers or polymers) of many linked units. The general chemical structure of a polymeric proanthocyanidin comprises linear chains of flavonoid 3-ol units linked together through common C(4)-C(6) and/or C(4)-C(8) bonds. 13C NMR has been useful in identifying the structures of polymeric proanthocyanidins, and recent work has elucidated the chemistry of di-, tri-, and tetrameric proanthocyanidins. Larger oligomers of the flavonoid 3-ol units are predominant in most plants and are found with average molecular weights above 2,000 Daltons and containing 6 or more monomer units (Newman, et al., Mag. Res. Chem., 25:118 (1987)).
Considerable recent research has explored the therapeutic applications of proanthocyanidins, which are primarily known for their antioxidant activity. However, these compounds have also been reported to demonstrate antibacterial, antiviral, anticarcinogenic, anti-inflammatory, anti-allergic, and vasodilatory actions. In addition, they have been found to inhibit lipid peroxidation, platelet aggregation, capillary permeability and fragility, and to affect enzyme systems including phospholipase A2, cyclooxygenase, and lipoxygenase. For example, proanthocyanidin monomers (i.e., anthocyanins) and dimers have been used in the treatment of diseases associated with increased capillary fragility and have also been shown to have anti-inflammatory effects in animals (Beladi, et al., Ann. N.Y. Acad. Sci., 284:358 (1977)). Based on these reported findings, oligomeric proanthocyanidins (OPCs) may be useful components in the treatment of a number of conditions (Altern. Med. Rev. 5(2):144-151 (2000)).
Proanthocyanidins may also protect against viruses. In in vitro studies, proanthocyanidins from witch hazel (Hamamelis virginiana) killed the Herpes simplex 1 (HSV-1) virus (Erdelmeier, C. A., Cinatl, J., Plant Med. June: 62(3):241-5 (1996); DeBruyne, T., Pieters, L., J. Nat. Prod. July: 62(7):954-8 (1999)). Another study was carried out to determine the structure-activity relationships of the antiviral activity of various tannins. It was found that the more condensed the chemical structure, the greater the antiviral effect (Takechi, M., et al., Phytochemistry, 24:2245-50 (1985)). In another study, proanthocyanidins were shown to have anti-Herpes simplex activity in which the 50 percent effective doses needed to reduce herpes simplex plaque formation were two to three orders of magnitude less than the 50 percent cytotoxic doses (Fukuchi, K., et al., Antiviral Res., 11:285-298 (1989)).
Cyclooxygenase (COX-1, COX-2) or prostaglandin endoperoxide H synthase (PGHS-1, PGHS-2) enzymes are widely used to measure the anti-inflammatory effects of plant products (Bayer, T., et al., Phytochemistry, 28:2373-2378 (1989); and Goda, Y., et al., Chem. Pharm. Bull., 40:2452-2457 (1992)). COX enzymes are the pharmacological target sites for nonsteroidal anti-inflammatory drugs (Humes, J. L., et al., Proc. Natl. Acad. Sci. U.S.A., 78:2053-2056 (1981); and Rome, L. H., et al., Proc. Natl. Acad. Sci. USA., 72:4863-4865 (1975)). Two isozymes of cyclooxygenase involved in prostaglandin synthesis are cyclooxygenase-1 (COX-1) and cyclooxygenase-2 (COX-2) (Hemler, M., et al., J. Biol. Chem., 25:251, 5575-5579 (1976)). It is hypothesized that selective COX-2 inhibitors are mainly responsible for anti-inflammatory activity (Masferrer, J. L., et al., Proc. Natl. Acad. Sci. U.S.A., 91:3228-3232 (1994)). Flavonoids are now being investigated as anti-inflammatory substances, as well as for their structural features for cyclooxygenase (COX) inhibition activity.
Due to the above characteristics and benefits of anthocyanins and proanthocyanidins, much effort has been put forth toward extracting these compounds from fruits, vegetables, and other plant sources. In addition to proanthocyanidins and anthocyanins, plants, fruits, and vegetables also contain other compounds such as mineral salts, common organic acids such as citric or tartaric acid, carbohydrates, flavonoid glycosides and catechins. It is often desirable to separate the anthocyanins and proanthocyanidins from other naturally occurring compounds. Anthocyanins have been extracted from plants and fruits by various procedures. One method of extracting anthocyanins employs the addition of bisulfate to form zwitterionic species. The extract is passed through an ion exchange column which adsorbs the zwitterionic anthocyanin adducts, and the adsorbed anthocyanins are eluted from the resin with acetone, alkali, or dimethylformamide (DMF). Disadvantages of this process include the presence of bisulfate, which interferes with adsorption of anthocyanins, thereby requiring multiple column adsorptions. Elution with alkali degrades the anthocyanins considerably, while DMF is not a recognized food additive and therefore must be completely removed before the anthocyanins can be added to any food products.
In order to capture these flavonoid compounds, well-defined and precise processing and separation techniques are needed. Nafisi-Movaghar, et al. in U.S. Pat. No. 5,912,363 describe a method for the extraction and purification of proanthocyanidins from plant material comprising heating an aqueous mixture of plant material, filtering the aqueous solution through an ultrafiltration membrane to remove larger molecular weight polymers and particulates to produce a permeate containing extracted proanthocyanidins, separating the proanthocyanidins from the liquid by contacting the permeate with an adsorbent material which is capable of releasably retaining the proanthocyanidins, and eluting the retained proanthocyanidins with a polar solvent. However, this method uses a very hot extraction temperature, which can cause degradation of the proanthocyanidins. Further, the ultrafiltration removes some of the low molecular weight polyphenolic material from the final product.
Many processes known in the art for extracting and isolating proanthocyanidins and/or anthocyanins from various plant materials use toxic and/or environmentally hazardous materials. Consequently, the current methods available for isolating and purifying proanthocyanidins are not easily scaled up to an efficient commercial process where disposal considerations of various chemicals and solvents play an important role in the overall feasibility of the process. Further, proanthocyanidins and anthocyanins must be isolated in a manner that minimizes their natural tendency toward degradation.
There is still a need, therefore, for an efficient process for isolating and purifying compositions containing phenolic compounds such as proanthocyanidins for uses in nutraceuticals and pharmaceuticals that is cost-effective, scalable, economically sound, does not require the use of toxic solvents or reagents, and isolates the phenolic compounds from plant material in a manner that minimizes their tendency toward degradation.